The present invention relates to a tubular casing, to a process for its manufacture, and to its use. More especially, the invention relates to a tubular casing suitable for smoked foodstuffs, especially sausages.
Tubular casings of this type are made by folding a web along the longitudinal axis to form a tube and gluing the overlapping edge zones running parallel to the longitudinal axis.
According to U.S. Pat. No. 2,607,696, an edge zone of the web of regenerated cellulose is provided with an acid aqueous solution of a partially polymerized, heat-curable resin and the other edge zone of the web is then pressed together with the resin layer, a tube being formed. Subsequently, the overlapping edge zones are joined to one another at about 180.degree. to 220.degree. C. under the action of pressure, whereby the resin is heat-cured. Examples of resins mentioned are urea/formaldehyde resins and melamine/formaldehyde resins. According to statements in this printed publication, this tubular casing can also be used as a sausage casing for the production of small skinless sausages, with the tubular casing being peeled off from the sausage after the boiling step.
This old process, which has been known for about 30 years, is hardly used any longer. In particular, the overlapping seam obtained is not sufficiently strong. Because of the relatively low breaking strength of the seam, there is, for example, an increased risk of bursting of the sausages made with this casing. Moreover, the known tubular casing can be manufactured only by a relatively complicated method. In particular, the high temperatures during the gluing lead to an undesired loss of water and to a permanent deterioration of the physical properties of the web material, so that the tubular casing obtained is not suitable, for example, for the subsequent shirring to produce shirred sticks. On the other hand, according to this printed publication, heating to temperatures of above 180.degree. C. is necessary after the application of adhesive, in order to obtain any bond at all between the mutually overlapping edge zones of the web. Additionally, this publication does not contain any indication to the effect that the seam region is adequately gas-permeable and smoke-permeable, which would enable these tubular casings to also be used for foodstuffs which are to be smoked.
Because of these disadvantages, tubular casings for foodstuffs, in particular artificial sausage casings, have in the meantime been manufactured predominantly from seamless material, although some disadvantages must be accepted in the case of these seamless tubular casings. In particular, this process is very cost-intensive.
Seamless tubes of fiber-reinforced regenerated cellulose are usually manufactured by the following essential process steps. A web of nonwoven fiber is formed to give the shape of a tube, the edge zones of the web overlapping and being glued with viscose. After one-sided or two-sided coating of the tube of nonwoven fiber with viscose from annular slot dies, the viscose is coagulated, regenerated to give cellulose hydrate gel and dried. Non-fiber-reinforced seamless tubes of regenerated cellulose are produced by extrusion of viscose through an annular die into the coagulation bath, and they are converted analogously into regenerated cellulose. During the coagulation and regeneration, the tube is supported by the gas mixture being formed and, during drying, it is supported by an enclosed volume of air which has been introduced. If appropriate, the tube is stretched in the longitudinal and transverse directions in order to improve its mechanical properties.
Disadvantageously, weakened zones, so-called spinning edges, which run parallel to the longitudinal axis in the edge region appear during the regeneration, for example, on the edges which result from the tube being laid flat.
Moreover, the stretching processes which are customary with seamless tubes also have disadvantages. Neither the internal pressure of the process gases evolving in the tube nor the internal pressure during drying can be controlled with sufficient accuracy, so that the diameter and the wall thickness of the seamless tubes cannot be kept constant within narrow limits, even if complicated and expensive process engineering is applied. A further disadvantage is that, when tubes are stretched by means of an expanding gas, the ratio of the stretching forces acting in the tangential and radial directions is fixed so that, for this reason, the mechanical properties of the seamless tube are also fixed, in particular the shrinking properties and the strength in the longitudinal and transverse directions.